I'll start with the turntable. The two you currently have are underwhelming, with the Technics SL-1900 having the most potential. For possible fixes for it please check out the sizable and knowledgable user community over at the Vinyl Engine forum. http://www.vinylengine.com/turntable_forum/viewforum.php?f=16

If the Technics is not salvagable, then I'd consider the Music Hall MMF-2.2, as the Rega RP-1 has quality issues and the Pro-Ject Debut III or Debut Carbon (and the Rega RP-1) do not have adjustable vertical tracking angle. The MMF-2.2 is more easily upgraded with a Pro-Ject Acryl-IT platter, Pro-Ject Speed Box II, and a wide variety of cartridges.

The Polk RTi4s are definitely replacable, although they might just be the best pieces you have. Are you sticking with bookshelf speakers or do you have room for floorstanders?

The Harman Kardon AVR 635 is compromised for a two-channel music system as it has superfluous video circuitry and impaired amplifier section. I'd look at replacing it as well.

$2,500? This would be a great start:

Music Hall MMF-2.2 LE in black $450 http://www.vinylengine.com/turntable_forum/viewtopic.php?t=17518 http://www.soundandvisionmag.com/article/face-best-turntable-budget

Emotiva USP-1 and XPA-200 $950 delivered http://www.hometheaterhifi.com/preamplifiers/preamplifiers-reviews/emotiva-usp-1-stereo-preamplifier.html http://www.tonepublications.com/review/the-emotiva-usp-1-preamplifier-and-upa-1-amplifiers/ http://shop.emotiva.com/products/xpa200

Magnepan MMG $600 floorstanders OR Ascend Acoustics CM-340 mains $608 bookshelves http://www.soundadviceblog.com/reviews/review-magnepan-mmg-speakers/ http://www.goodsound.com/equipment/magnepan_mmg.htm http://hometheaterreview.com/magnepan-mmg-floor-standing-speakers-reviewed/  http://www.ascendacoustics.com/pages/reviews/aa2007-04.pdf  http://www.hometheatersound.com/equipment/ascend_cmt340se_cbm170se.htm http://www.3luxe.com/best_ofs/Surround_Sound_Speakers/Ascend_Acoustics_CMT-340_SE_and_CBM-170_SE

All of it except the turntable you can listen to for a while in your own home, and if you don't want it, return it for a purchase price refund.

the music hall mmf 2.2 on the recommendation of many here